Persons using biocidal agents in the biocidal treatment of water customarily, if not universally, refer to xe2x80x9cfree chlorinexe2x80x9d level as a measure of biocidal control. To achieve xe2x80x9cfree chlorinexe2x80x9d levels in water treatment, solid materials are often preferred because of their high weight percent activity. N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) has been one of the most widely-used solid sources of xe2x80x9cfree chlorinexe2x80x9d for water treatment. One of the features emphasized for BCDMH by suppliers of BCDMH is that in use, the combined chlorine from the biocide regenerates xe2x80x9cfree chlorinexe2x80x9d by reaction with inactive bromide species formed during the water treatment operation. In other words, the chlorine atom in the initial N,Nxe2x80x2-bromochloro-5,5-dialkylhydantoin is said to be a precursor for additional xe2x80x9cfree chlorinexe2x80x9d for sanitation purposes.
While effective, BCDMH does have certain heretofore-unrecognized drawbacks. For example, when used at conventional dosage levels in treating industrial water systems, the rate of corrosion of iron and copper surfaces in contact with the treated water is higher than desired. In addition, the rate of consumption of the BCDMH in treating the water for effective biocidal action is significantly higher than is desirable from the standpoint of the consumer. Further, during usage the amount of halogen residual in the treated water is lower than would be desired.
Further shortcomings of BCDMH are that in use, BCDMH hydrolyzes into HOBr and HOCl both of which register as xe2x80x9cfree chlorinexe2x80x9d species in commonly-used standard test procedures. These methods for determining xe2x80x9cfree chlorinexe2x80x9d levels in treated water, involve use of a reagent known as DPD (i.e., N,Nxe2x80x2-diethyldiphenylenediamine) and a buffer, and the results of such analyses are commonly used, if not universally used, as the basis for determining the quantity of a halogen-containing microbiocidal agent to be used for water treatment. Heretofore, consumers of BCDMH have only been concerned with the level of xe2x80x9cfree chlorinexe2x80x9d provided by a given quantity of that biocidal material. What has not been realized by such consumers is the amount of xe2x80x9ctotal chlorinexe2x80x9d being utilized in order to achieve the requisite xe2x80x9cfree chlorinexe2x80x9d level. As a consequence, the consumer has not had available a yardstick by which to determine the true economic efficiency of using BCDMH as a biocidal agent in the treatment of water. To achieve optimum economic efficiency, the consumer should have available for use a biocidal agent in which the amount of xe2x80x9cfree chlorinexe2x80x9d released into the water corresponds closely to the xe2x80x9ctotal chlorinexe2x80x9d content of the biocidal agent.
In the event a biocidal agent provides a relatively small amount of xe2x80x9cfree chlorinexe2x80x9d in relation to its xe2x80x9ctotal chlorinexe2x80x9d content, it has been deemed necessary to utilize a relatively large amount of such agent in order to achieve microbiological control. This in turn means high levels of halogenated materials are released into the environment. If on the other hand, a biocidal agent could provide to the water an amount of xe2x80x9cfree chlorinexe2x80x9d that closely corresponds to the xe2x80x9ctotal chlorinexe2x80x9d content of the biocidal agent, effective microbiological control could be realized by use of much smaller dosages and with consequent minimal adverse impact upon the environment.
Also, while reasonably effective as a microbiocide, BCDMH is not as effective against biofilms tested to date as would be desired. Biofilms are bacterial films which tenaciously adhere to surfaces in contact with water such as heat exchanger surfaces, conduit interiors, filters, and other processing equipment. These films are very undesirable because they can harbor dangerous pathogens, and cause damage to the surfaces to which they have become attached. Moreover, the bacteria form a slime layer of extra-cellular polysaccharide which affords protection to the bacteria and in addition constitute an effective barrier against penetration of biocidal agents used in an attempt to combat such bacteria. In situations where the water is prone to development of calcium carbonate scale, the presence of such gelatinous extra-cellular polysaccharides can result in the formation of layers of scale bonded to the substrate surface by the gelatinous polysaccharides. Polysaccharide films and films of scale bonded by means of polysaccharides can greatly interfere with the operation of heat exchangers by virtue of their insulating characteristics, and can markedly interfere with the functioning of filters and the flow of water through pipes and conduits by virtue of the clogging tendencies of such polysaccharide films.
It would therefore be of considerable advantage if these drawbacks could be avoided in actual practice.
This invention involves, inter alia, the discovery not only of the existence of a number of these drawbacks, but that it is indeed possible to avoid each and every one of these drawbacks in a highly efficient manner. Moreover, this invention makes it possible to continuously and inexpensively dose water in contact with biofilm, or that comes into contact with biofilm, using a highly effective biocide that provides very effective microbiocidal control of planktonic microorganisms and of biofilm species, even where the biofilm infestations have been in existence for long periods of time and thus have encased themselves in a substantial quantity of slimy defensive polysaccharide layers or films.
Accordingly, in one of its embodiments this invention provides a method of achieving highly effective xe2x80x9cfree chlorinexe2x80x9d levels in treating with a biocide water that is or that comes into contact with at least one iron or copper surface, which method comprises introducing into said water, preferably but not necessarily continuously or substantially continuously, an effective biocidally active amount of at least one 1,3-dibromo-5,5-dialkylhydantoin that provides in the water a highly effective xe2x80x9cfree chlorinexe2x80x9d level that is within 90% of the xe2x80x9ctotal chlorinexe2x80x9d level of the water, and that reduces the rate of corrosion of said iron or copper with which the water is or comes into contact as compared to N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin.
In another of its embodiments this invention provides a method of achieving highly effective xe2x80x9cfree chlorinexe2x80x9d levels in treating water with a biocide, which method comprises introducing into said water, preferably but not necessarily continuously or substantially continuously, an effective biocidally active amount of at least one 1,3-dibromo-5,5-dialkylhydantoin that provides in the water a highly effective xe2x80x9cfree chlorinexe2x80x9d level that is within 90% of the xe2x80x9ctotal chlorinexe2x80x9d level in the water, and that enables the rate of biocide consumption to be reduced as compared to N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin. In this embodiment it is further preferred that the water being treated is or comes into contact at least one surface of iron or copper so that the rate of corrosion of said iron or copper is reduced as compared to N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin.
In each of the above embodiments it is particularly preferred to effect the introduction of the 1,3-dibromo-5,5-dialkylhydantoin(s) into the water continuously or substantially continuously by use of a dispenser, especially a floating dispenser, containing the 1,3-dibromo-5,5-dialkylhydantoin(s), more preferably in granular form.
The granules of 1,3-dibromo-5,5-dialkylhydantoin(s) used in the dispenser can be granules formed with or without use of one or more added substances contributing binding strength to the granules.
Still more preferably the granules of 1,3-dibromo-5,5-dialkylhydantoin(s) used in the dispenser are granules of this invention having one or both of the following characteristics and even more preferably both of the following characteristics:
a) an average crush strength of at least about 15 pounds per inch of thickness; and
b) an average size in the range of about 40 U.S. standard mesh size to about xe2x85x9c-inch.
In another preferred embodiment the granules of this invention used in the dispenser are formed using a non-hydrophobic added substance contributing binding strength to the granules. The term xe2x80x9cnon-hydrophobicxe2x80x9d is used herein to denote that the added substance in the amount present in the granules should not prevent, because of its resistance toward water, the granules from releasing to the water enough biocidal species (e.g., xe2x80x9cfree brominexe2x80x9d) to provide an acceptable amount of biocidal activity in the water being treated. Thus while the added substance in its pure state may be hydrophobic, if used in a small enough amount as not to prevent the granules from releasing to the water enough biocidal species (e.g., xe2x80x9cfree brominexe2x80x9d) to provide an acceptable amount of biocidal activity in the water being treated, the substance is deemed xe2x80x9cnon-hydrophobicxe2x80x9d when used in such an amount.
In yet another preferred embodiment the granules of this invention used in the dispenser are formed using a suitable binder quantity of a micronized synthetic polyolefin-based hydrocarbon wax and/or a micronized synthetic polyfluorocarbon wax. These waxes so used are compatible with the active ingredient. In still another preferred embodiment the granules of this invention used in the dispenser are free of any added substance contributing binding strength or hardness to the granules.
The 1,3-dibromo-5,5-dialkylhydantoin(s) used in the practice of the various embodiments of this invention are typically those in which one of the alkyl groups in the 5-position is a methyl group and in which the other alkyl group in the 5-position has in the range of 1 to 4 carbon atoms. Most preferred for this use is 1,3-dibromo-5,5-dialkylhydantoin.
Other embodiments include a biocidal composition which comprises granules of at least one 1,3-dibromo-5,5-dialkylhydantoin having a crush strength of at least 15 pounds per inch of granule thickness, and preferably at least 20 pounds per inch of granule thickness, and an average size in the range of about 40 U.S. standard mesh size to about xe2x85x9c-inch, such 1,3-dibromo-5,5-dialkylhydantoin(s) being characterized in that one of the alkyl groups in the 5-position is a methyl group and the other alkyl group in the 5-position has in the range of 1 to 4 carbon atoms, the granules being devoid of any additive therein conferring binding or hardening action to the granules. A particularly preferred composition of this type is one in which the at least one 1,3-dibromo-5,5-dialkylhydantoin is 1,3-dibromo-5,5-dimethylhydantoin and in which the granules are able to be dissolved in quiescent water that is at a temperature of 25xc2x0 C. at a rate such that 60 minutes after immersing the granules in quiescent water, the water contains in the range of about 75 to about 430 mg/L of xe2x80x9cfree chlorinexe2x80x9d per gram of granules that were immersed in the water.
Other embodiments, features, and advantages of this invention will be still further apparent from the ensuing description and appended claims.